Hey Micheal,
I slept around friends' houses quite a few times pre-op, and also shared a tent sleeping compartment with a friend for a few days too.
I'd sleep in a baggy t-shirt or button up, though I was C cup so that alone definitely wouldn't hide everything.
So while sleeping over I would have a large-ish backpack with me that had my clothes and stuff in. Upon getting up I'd pick up the bag as I stood and carry it in front of me against my chest on my way to the bathroom. Get changed etc there, nobody should think anything of it.
With the tent I'd literally have to wait until my friend got changed and left the sleeping compartment. Then zip it up and shove my binder on there. For that you'd have to be able to put your binder on while sitting at least.
Oh, I also shared an 8 person hostel room for a couple of nights [4 friends and 4 strangers], but luckily each bed had it's own curtain, so I just dressed behind mine after getting into bed.
Have fun on your trip, and don't worry about it too much! People are sleepy at night and in the morning, nobody pays too much attention to anything anyways. :p